Fruitadens: how small can a dinosaur get?

Dinosaurs have become known, for the most part, as huge reptiles from the past. Huge carnivores like Tyrannosaurus rex would have been chasing hadrosaurs, like Parasaurolophus, and ceratopsids, like Triceratops. Gigantic battles may have been waged, with the outcome being life or death struggles. While this paints an incredible picture and is commonly what people think of when hearing the word "dinosaur", many others realize that dinosaurs could also be quite small. Velociraptor, of Jurassic Park fame, was not actually very large, with adults measuring 6-7 feet long (including the tail), protoceratopsids (small relatives of Triceratops) were only roughly sheep-sized and grew to about 6 feet with their tails included. While these are slightly more well-known, various other dinosaurs stayed diminutive compared to the larger things around them.

In the Late Jurassic (around 150 Mya) of the USA, famous dinosaurs such as Allosaurus, Stegosaurus, Apatosaurus (= Brontosaurus), and Brachiosaurus were roaming the American west. Running around their feet, and doing their best not to get trampled, was a tiny dinosaur named Fruitadens haagarorum, named by Butler and colleagues in 2010). Fruitadens was a tiny, plant-eating dinosaur from the group known as heterdontosaurids. 

Artist’s reconstruction of Fruitadens ( by Smokeybjb, and licensed under Creative Commons Attribution-Share Alike 3.0 Unported license.)

Heterodontosaurids were a group of plant-eating ornithiscians related to iguanodontids (like Iguanodon) and hadrosaurids (like Parasaurolophus and Edmontosaurus), among others. These dinosaurs were commonly fairly small, and had "fangs" towards the front of their mouths.You should be able to see the fangs if you look close enough at the reconstruction. They actually get their name from their strong heterodont dentition. Even so, their morphology is relatively generalized, suggesting more of an omnivorous lifestyle, with plants, insects, and some other small organisms making up the majority of their diets.

Fruitadens was named based on a few individuals (4), but the holotype consists of incomplete jaws, several vertebrae, and partial hind limbs of a nearly full grown individual. This was sufficient, however, to determine that it was, indeed, something unique and new.

Reconstructed skull of Fruitadens (Butler et al., 2012)

Fruitadens was estimated by Butler et al. (2010) to have only been about 28 cm long (less than a meter) and weighed less than 1 kg (less than 2 lbs)! That size estimate is quite incredible, especially for a dinosaur that is thought to be nearly full-grown. Overall size would have probably not changed at all, or at least very little, once it became fully mature!

Full-size Fruitadens haagarorum model with co-author Luis Chiappe (from AP).

But why bring this up now if this dinosaur was named in 2010? In the original publication, Butler et al. (2010) were unable to go into much detail regarding the description and morphology of this new taxon. But a new, thorough study just published by Butler et al. (2012) has given this small dinosaur its descriptive due. The new study seeks to document this dinosaur in great detail, giving new information not only on Fruitadens, but also on the whole heterdontosaurid family of dinosaurs. This study helps us understand a group of dinosaurs that were not very well known before, and helps clarify a picture that can seem somewhat blurry at times (or all the time...).

This seems to be an excellent example of a taxon that was named in a relatively short paper, but then had a follow-up study to give us a much clearer picture of exactly what it was/is. Too often taxa (not just dinosaurs) are named in short papers or with short blurbs. Little detail is given, and sometimes proper diagnoses are not even provided. I can't tell you how many times I have come across taxa and, when going to the original publications, I find little information other than the name itself. And, going a step further, often times little work has been done on the taxa after the initial publication. This was far worse decades ago and has gotten better since, but various examples can be found still today (e.g. Atrociraptor) with little work done on the taxa themselves and more work done regarding their inclusion in cladograms.

Depiction of some of the largest known hadrosaurs and, therefore, some of the largest known ornithischians, with a adult male for scale

Depiction of Fruitadens haagarorum, with a portion of an adult male for scale

References:

Butler RJ, Galton PM, Porro LB, Chiappe LM, Henderson DM, Erickson GM (2010) Lower limits of ornithischian dinosaur body size inferred from a diminutive new Upper Jurassic heterodontosaurid from North America. Proceedings of the Royal Society B 277: 375–381.

Butler RJ, Porro LB, Galton PM, Chiappe LM (2012) Anatomy and cranial functional morphology of the small-bodied dinosaur Fruitadens haagarorum from the Upper Jurassic of the USA. PLoS ONE 7(4): e31556. doi:10.1371/journal.pone.0031556

Miracinonyx: American cheetah or something else.....

This will be a somewhat short post on a subject that has intrigued me for quite awhile. Not that long ago, geologically speaking, North America was home to numerous felids (cats). While ones that many people know of were present, such as Lynx (bobcat and lynx), Puma (mountain lion) and Panthera onca (jaguar), several others were present that are no longer around. These include, among others, Smilodon (saber-toothed cat), Panthera atrox (American lion), and Miracinonyx (American cheetah). Here, we fill focus briefly on the final one listed, Miracinonyx.

The Carnivores of Rancho La Brea.
From left to right. The dire wolf (Canis dirus), the sabre-toothed cat (Smilodon fatalis), the short-faced bear (Arctodus simus), the cheetah-like cat (Miracinonyx sp.), and the American lion (Panthera atrox). Modified from Turner, A., and Anton, M., The Big Cats and Their Fossil Relatives. Columbia University Press: New York, 1997.

Miracinonyx, commonly called the American cheetah by some, has been found various places throughout North America. Cope (1895) named Uncia inexpectata from some isolated teeth from a cave in Pennsylvania. A second species was named "Felis" studeri from Texas by Savage (1960). Both these would eventually be referred to the genus Miracinonyx (aka American cheetah). Both these taxa were alive pre-Rancholabrean (>240,000 ybp), and Kurten (1976) synonymized both felids with the idea that there was only one Miracinonyx species before the Rancholabrean. Not long after the erection of studeri, Orr (1969) named "F." trumani baed on a skull from a cave in Nevada.

Adams (1979) grouped these taxa together within Acinonyx, the genus of the modern cheetah, due to morphological similarities. He went a step further, however, and grouped them in the subgenus Miracinonyx. The taxonomy of these cats was in a state of flux for awhile, with numerous workers considering the only valid genera to be A. studeri and A. trumani. Van Valkenburgh et al. (1990), however, reported on a remarkable specimen from Hamilton Cave in West Virginia, and concluded that, while A. trumani was valid, it was A. inexpectatus that was the second valid species, with A. studeri as its junior subjective synonym.They also elevated Miracinonyx to the generic level. Van Valkenburgh et al. (1990) were also keen to call them American "cheetah-like cats" rather than American "cheetahs".

Osteological reconstruction of Miracinonyx inexpectatus based on material from Hamilton Cave, West Virginia. Scale = approximately 240 cm (from Van Valkenburgh et al., 1990).

Miracinonyx inexpectatus is the species that first came to be viewed as the "American cheetah". In many ways, the cranial and post-cranial morphology were quite reminiscent of cheetahs today. They have been also, however, commonly compared to Puma, and many researchers have debated which they are more closely related to. While M. inexpectatus had longer and somewhat gracile limbs, M. trumani was, in comparison, a smaller and relatively more robust cat. 

Phylogenetic relationships of the Miracinonyx-Acinonyx lineage based on 27 morphological characters with Leopardus pardalis as the outgroup (from Christiansen and Mazak (2009)).

Miracinonyx has been considered more of a plains species, commonly using Acinonyx (cheetah) as a modern analogue. This is true for both species, even though M. trumani is less similar to Acinonyx than M. inexpectatus, and seems to be more similar morphologically to Puma. This was discussed not long ago by J.P. Hodnett. Hodnett, in an upcoming study, discusses remains of M. trumani from caves in the Grand Canyon of Arizona. Rather than living in a plains habitat, it seemed to be living in a more mountainous terrain with lots of elevation change. 

Adult Snow Leopard (Uncia uncia)

Hodnett took it a step further though, and compared Miracinonyx trumani to the ultimate modern felid adventurer, Uncia uncia, or the snow leopard. He felt that, in order to be agile and a top predator in the Grand Canyon, that M. trumani would have been behaving similar to the snow leopard. 

So, Miracinonyx similar to the snow leopard? It seems like a bit too extreme. Puma behaves, in some ways, similar to Uncia, although in many ways the former is more of a habitat generalist, doing well in a wide variety of habitats throughout North America. Acinonyx, on the other hand, is specialized for open habitat, and Uncia tends to stick to mountainous areas.

With that being said, is Miracinonyx still the American cheetah? Is it the "American Puma"/ancient ancestor of the modern Puma? Or could it be the American snow leopard? While I would lean towards it being more of a generalist like the puma, it could also turn out that M. inexpectatus behaved like the cheetah, while M. trumani behaved like the mountain lion, so one answer will not suffice. Presumably, time and further research will tell us the answer.

References:

 

Adams, D.B. 1979. The cheetah: native American. Science 205:1155-1158.

Christiansen, P. and Mazák, J.H. 2009. A primitive Late Pliocene cheetah, and evolution of the cheetah lineage. Proceedings of the National Academy of Sciences 106(2):512-515.

Cope, E.D. 1895. The fossil vertebrates from the fissure at Port Kennedy Cave, Pennsylvania. Proceedings, Academy of Natural Sciences, Philadelphia 1895:446-451.

Hodnett, J-P., White, R.S., Carpenter, M., and Mead, J.I. in prep. Miracinonyx trumani (Carnivora: Felidae) from the Rancholabrean of the Grand Canyon, Arizona and its implications on the ecology of the “American cheetah”.

Kurtén, B. 1976. Fossil puma (Mammalia: Felidae) in North America. Netherlands Journal of Zoology 26:502-534.

Orr, P.C. 1969. Felis trumani a new radiocarbon dated cat skull from Crypt Cave, Nevada. Bulletin of the Santa Barbara Museum of Natural History Department of Geology 2:1-8.

Savage, D.E. 1960. A survey of various late Cenozoic vertebrate faunas of the panhandle of Texas. Part III, Felidae. University of California Publications in Geological Sciences 36:317-343.

Turner, A. and Anton, M. 1997. The Big Cats and Their Fossil Relatives. Columbia University Press, New York. 234 pp.

Van Valkenburgh, B. Grady, F. and Kurtén, B. 1990. The Plio-Pleistocene cheetah-like cat Miracinonyx inexpectatus of North America. Journal of Vertebrate Paleontology 10(4):434-454.